1. Field of the Invention
The field of this invention is apparatus and methods for providing pressurized pulverized solid fuel to a reactor.
2. Description of the Prior Art
In supplying pulverized solid fuel, such as lignite or hard coal, to a high-pressure coal gasification reactor, the gas pressure in the reactor, which is generally at least 10 atmospheres absolute (atm. abs.), has to be overcome. Another problem connected with this supply is the high temperature of the reactor wall. In order to solve these problems, it has been suggested heretofore that the pressurizing of the coal powder be separated from its introduction into the reactor. In this way the coal powder is pressurized in a vessel and subsequently passed from the vessel to the reactor. The pressure in the vessel will be at least equal to the reactor pressure. As a rule, the coal powder is mixed with the air or oxygen required for the gasification before the powder enters the reactor. In view of the relatively long residence time of the coal powder in the mixing vessel, an explosion hazard is created under such conditions, so the mixing is usually effected in the reactor or burner. The solid fuel is fed by a dosing or feeding apparatus which may be, for example, a screw conveyor which debouches or discharges the solid fuel into the burner of the reactor, into which air or other oxygen-containing material is also fed through a separate line. However, other designs are equally possible; for example those in which the coal particles are fluidized in the vessel and in which the coal particles are withdrawn from the vessel as a fluidized stream and supplied to a burner, with the required air or oxygen.
The vessel is usually pressurized with a gas which is inert to fuel powder, i.e. which contains little or no oxygen, and which usually has a low or relatively low temperature in comparison with the temperatures in the gasification reactor. Suitable gases for this purpose are, for example, nitrogen, carbon dioxide, hydrogen, carbon monoxide, gaseous hydrocarbons and steam. Mixtures of these gases, with each other and/or with other gases, may also be used; as well as gas that has been obtained by the coal gasification and cooled. This inert gas is introduced into the vessel by another route than the powder. Preferably, the powder in such a vessel is in a more or less fluidized state.
Other processes than the above-mentioned coal gasification process also utilize an intermediate vessel in which fuel powder resides for some time in a gas-pressurized state.
In U.S. Pat. No. 3,182,825, an apparatus is disclosed wherein a rotor having centrifugal nozzles tapering outwards and arranged radially relative to its axis of rotation is used to inject powder into a vessel. A disadvantage of such nozzles is that they are liable to blockage by bridging--i.e. local compaction--of the powder flowing through. In that case there are few if any possibilities of removing these blockages during operation.